Method of producing cis-1,4 polybutadiene



United States Patent G 3,419,539 METHOD OF PRODUCING CIS-1,4 POLYBUTADIENE Kenichi Ueda, Hidetoshi Yasunaga, Koei Komatsu, and Jun Hirota, Yokkaichi-shi, Japan, assignors to Japan Synthetic Rubber Co., Ltd., Tokyo, Japan, a corporation of Japan No Drawing. Filed Mar. 16, 1966, Ser. No. 534,682 Claims priority, application Japan, Mar. 18, 1965, 40/15,575 9 Claims. (Cl. 260--94.3)

ABSTRACT OF THE DISCLOSURE A method for producing polybutadiene of high cis-1,4 content by polymerizing butadiene in the presence of a hydrocarbon solvent, an inert atmosphere and a catalyst at a temperature between -50 and 150 C. The catalyst is a mixture of an aluminum halide and a nickel oxide of the formula Ni O wherein x is 1 or 2, y is in the range of 1 to 3 and the ratio of y to x is 1-1.5:1, but excluding a ratio of l: 1.

This invention relates to a method of producing cis' 1,4 polybutadiene. More particularly it relates to a method of producing a butadiene polymer having a high percentage of cis-1,4 configuration using a novel polymerization catalyst.

The mechanical, physical and other properties of the vulcanized product of cis-1,4 polybutadiene having a high percentage of cis-1,4 configuration have proven for the last several years that such a polymer is superior as a general purpose rubber.

It has been heretofore known that cis-l,4 polybutadiene can be produced by contacting butadiene in the presence of non-aqueous medium with a catalyst such as (1) a reaction mixture of a salt of a metal of Group VIII of the Periodic Table and an organometallic compound, particularly an organometallic halogen compound of a metal of Group I, II or III of the table, (2) a reaction mixture of a salt of a metal of Group VIII of the table, an organometallic compound of a metal of Group I, II or III of the table and a Lewis acid, and (3) a reaction mixture of an organometallic compound of a metal of Group 1, II or III of the table and a Lewis acid.

All of the above-mentioned catalytic systems are socalled Ziegler type catalysts, which contain, as one component of the catalyst, an organometallic compound. As is well known, since organornetallic compounds react violently with oxygen or moisture in the air, their handling is very difficult, and even when they are stored under an inert atmosphere, they deteriorate by reacting with trace amounts of oxygen or moisture present in the inert gas. Therefore, these organometallic compounds are produced only with great difiiculty and are very expensive. Further, such deterioration of organometallic compounds or of reaction mixtures comprising these organometallic compounds during their storage results in poor reproducibility of polymerization velocity and of molecular weight and various other properties of the polymer produced thereby.

There have been known two methods of polymerizing butadiene with catalysts containing no organometallic compounds to obtain sis-1,4 polybutadiene. Japanese Patent Publication 9,443/ 63 discloses a method which comprises contacting butadiene with a three-component catalyst consisting of (a) at least one metal or anhydrous compound of divalent transition metals, i.e. cobalt, nickel, chromium, iron, manganese, palladium and platinum, (b) an anhydrous aluminum halide and (c) a proton acceptor. In this method, a temperature of higher than C. is required for the preparation of the catalyst, and the polymerization velocity is low. Japanese Patent Publication 20,826/64 discloses a method of polymerizing butadiene with a catalyst prepared by mixmg at a temperature from 20 to C. (a) an aromatic hydrocarbon solvent selected from the group consisting of benzene, alkylbenzenes and monohalo-nuclear substituted products thereof, (b) aluminum metal, (c) a cobaltous halide and (d) a hydrogen halide or mercuric halide. Polybutadiene produced by this method contains a large amount of gel.

An object of this invention is to provide a method of polymerizing butadiene using a novel catalyst containing no organometallic compound.

Another object of this invention is to provide a novel method of polymerizing butadiene, which has none of the disadvantages as above-mentioned.

Other and further objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the accompanying disclosure.

We have now discovered that a butadiene polymer having a high percentage of cis-1,4 configuration can be produced by contacting butadiene in the presence of a hydrocarbon solvent at a temperature between 50 C. and 150 C. under an inert gas atmosphere with a catalyst prepared by mixing, under controlled conditions in a hydrocarbon solvent under an inert gas atmosphere, (1) a halide of aluminum and (2) an oxide of nickel of the formula Ni O wherein x is an integer from 1 to 2, y is in the range of l to 3 and the ratio of y to x is in the range of 11.5 :1, but excluding a ratio of 1:1 and wherein said oxide of nickel contains no active .oxygen capable of oxidizing potassium iodide at room temperature.

We have already provided a method of producing cis-1,4 polybutadiene with a catalyst prepared by mixing an aluminum halide and a nickel peroxide which contains at least 0.1 milligram equivalent of active oxygen, per gram of the peroxide, capable of oxidizing potassium iodide at room temperature (U.S. patent application No. 450,184, filed on Apr. 22, 1965).

We had believed that the nickel peroxide in this catalyst system had to contain at least 0.1 milligram equivalent of the active oxygen per gram of the peroxide to produce cis-1,4 polybutadiene, because the usual nickel oxide (NiO) does not contain any active oxygen and the catalyst consisting of nickel oxide and aluminum chloride gives oily polymers having a low cis-1,4 configuration with low polymerization activity.

But we have unexpectedly discovered that an oxide of nickel having the formula Ni O of the present invention is effective for the production of polybutadiene having a high percentage of cis-1,4 configuration, though it does not contain any such active oxygen.

Oxides of nickel which can be used as one component of the catalyst of the present invention are represented by the formula Ni O wherein x is an integer from 1 to 2, y is in the range of 1 to 3 and the ratio of y to x is in the range of 11.5: l, but excluding a ratio of 1:1. The valency state of nickel of the oxides of the present invention is higher than II. Namely these oxides have excess oxygen compared with nickel oxide (NiO). These oxides are well known and are defined as the Bertholide compound [G. Hagg; Acta Chem. Scand, 4, 88 (1950)].

These oxides of nickel can usually be prepared by heating or thermally cracking an inorganic salt of divalent nickel at a temperature below 700 C. in the presence of oxygen or air, or in vacuo.

Commercially available nickel black, which is believed to have the molecular formula Ni O can also be used in this invention.

Among the inorganic salts of divalent nickel, nickel nitrate, nickel sulfate, nickel phosphate, nickel fluoride, nickel chloride, nickel bromide, nickel iodide and nickel hydroxide are preferable. Nickel nitrate and nickel hydroxide are particularly preferable.

The temperature of the heating or thermal cracking must not be higher than 700 C., since at temperatures higher than 700 C., nickel oxide (NiO) is formed.

In general the ratio of y to x of the formula Ni O varies depending on both the temperature and the time of the heating or thermal cracking. For example, when nickel nitrate is oxidized in an oxygen stream at 550 C. for 2 hours, an oxide of nickel having a ratio of yzx of from 1.05 to 1.20 is obtained. When the same oxidation is carried out at 350 C., an oxide of nickel having a ratio of yzx from 1.15 to 1.50 is obtained. A temperature between 200 C. and 600 C. is usually preferred for the heating or thermal cracking. But when an oxide of nickel having a large y:x ratio, e.g. from 1.35 to 1.50, is desired, a temperature below 200 C. is suitable, but requires a long period of time, usually more than 5 hours for the heating or thermal cracking.

These oxides of nickel have the color of black or gray, and not the usual green of nickel oxide (NiO).

Furthermore these oxides of nickel may be prepared by heating at suitable temperature, for example at 200 C., nickel peroxides which contain at least 0.1 milligram equivalent of active oxygen, per gram of the peroxide, capable of oxidizing potassium iodide at room temperature. The thusly produced oxides of nickel have a gray color and do not contain any appreciable amount of such active oxygen.

Halides of aluminum which are another catalyst com ponent of this invention are anhydrous aluminum chloride, aluminum bromide and aluminum iodide. In general it is desirable that these halides be highly purified before use.

The catalyst of this invention can be prepared by mixing the two catalyst components described above at under controlled conditions in a hydrocarbon solvent under an inert gas atmosphere. The two catalyst components react with each other, and the color of the reaction mixture changes from yellow to brownish black. The resulting reaction mixture has polymerization activity. Though the conditions of the catalyst preparation can be varied depending upon the nature of the catalyst components, the desired polymerization conditions and so on, the catalyst is preferably prepared by contacting the two components at a temperature between 20 C. and 150 C. for from 1 to 500 minutes.

The proportion of the halide of aluminum to the oxide of nickel can be varied over a Wide range, but preferably is in the range of 0.1 to 10.0, more preferably is in the range of 0.5 to 3.0, based on the mole ratio of aluminum atom to nickel atom.

The polymerization reaction of the invention can be carried out as a batch or continuous process in the presence of a hydrocarbon solvent at a temperature between 50 C. and 150 C., preferably between 0 C. and 100 C., under an inert gas atmosphere.

Hydrocarbon solvents which are used for the catalyst preparation and polymerization reaction are aromatic, aliphatic and alicyclic hydrocarbons. Suitable solvents include aromatics such as benzene, toluene and xylene, aliphatics such as pentane, hexane, heptane, octane, nonane, decane, butane and propane, and alicyclics such as cyclohexane and cyclopentane. A mixture of these hydrocarbons can also be used as the solvent.

Generally it is advantageous to use the same hydrocarbon solvent for both the catalyst preparation and for the polymerization process, however different hydrocarbon solvents can, of course, be employed in the two steps. Aromatic hydrocarbons are most preferable for the catalyst preparation,

The polymerization reaction is carried out in the presence of from about 0.5 to about 50 parts by volume of hydrocarbon solvent per part by volume of butadiene.

The polymerization must be carried out under an inert gas atmosphere such as nitrogen, helium and argon.

The polymerization reaction can be carried out under autogeneous pressure or any suitable pressure sufiicient to maintain the reaction mixture substantially in the liquid phase.

The amount of catalyst to be used can be varied over a wide range depending upon the conditions of the catalyst preparation and polymerization reaction. Preferably the amount of the catalyst is in the range of 0.1 to 200, more preferably 1.0 to 100 millimoles based on the oxide of nickel per 10 moles of butadiene.

At the completion of the polymerization reaction, the catalyst is inactivated by adding water, alcohol, acetone or other inactivating agents to the polymerization system. There is also added to the polymerization system an antioxidant such as phenyl-B-naphthyl amine.

The resulting polybutadiene is coagulated by adding a poor solvent such as alcohol to the polymerization system, or by removing the solvent through steam distillation, and is then separated, washed and dried as usual.

The thus produced polybutadiene has at least percent of cis-1,4 configuration. It can be compounded and vulcanized by any of the known methods and used as a general purpose rubber in various fields.

The two catalyst components of this invention are readily available and are inexpensive. Also, the catalyst preparation is easy.

Another advantage of this invention is that both the catalyst and the components thereof can be stored for a long period of time and can be handled safely.

Another advantage of this invention is that a high cis- 1,4 polybutadiene which is gel free can be produced with good reproducibility and high polymerization activity.

A more comprehensive understanding of this invention can be obtained by referring to the following illustrative examples which are not intended, however, to be unduly limitative of the invention.

In the examples, the microstructure of the polymer was analysed according to the D. Morero Method [Chemica Lindustria, 91, 758 (1959)] by infra-red spectra analysis.

Intrinsic viscosity [1;] (dl./ g.) was measured at 30 C. in toluene.

Analysis of oxides of nickel was made by determining nickel with the EDTA Method and by determining oxygen by elemental analysis.

Active oxygen capable of oxidizing potassium iodide at room temperature was determined by potentiometric titration.

Example 1 Under an atmosphere of nitrogen from which oxygen and moisture were completely eliminated by passage through anhydrous calcium chloride, molecular sieves and then triethyl aluminum solution (0.5% by weight tetraline solution), 26.60 grams of toluene sufliciently dried by distillation in the presence of metallic sodium was introduced into a milliliter pressure-resistant reaction vessel with a syringe from the top of the vessel.

Then 0.06829 gram of anhydrous aluminum chloride sufficiently purified by sublimation and 0.0377 gram of an oxide of nickel having the molecular formula NiO were added to the vessel.

The oxide of nickel was produced by heating crystalline nickel nitrate in an oxygen stream at 550 C. for minutes. It was confirmed that the oxide of nickel had the molecular formula NlO and had no active oxygen.

Following this charge, the vessel was sealed with a crown cap having a butyl rubber packing under a nitrogen gas atmosphere. Then the reaction vessel was placed in a 6 thermostat of 60:05 C. After 60 minutes, the color of about 61% of cis-1,4, about 31% of trans-1,4 and the the reaction mixture turned to brownish black. At this balance of vinyl. Therefore it is clear that nickel oxide time the reaction vessel was taken out of the thermostat. (NiO) cannot be used for the catalyst of this invention.

The crown cap was removed therefrom under a nitrogen Example 14 gas atmosphere, and the reaction vessel was immersed in a dry ice-methanol bath of 80 C. 6.65 grams of The earelyst was P p y Contacting 010293 gram butadiene which was purified by passage through granular of an OXlde of nickel having e molecular formula potassium hydroxide, calcium chloride, granular potasms and 0:9639 g f nilnum chloride at 60 sium hydroxide and molecular sieves in that order, were for 2 hours 111 tolueneintroduced into the reaction vessel by distillation. Then The oxide of nickel was Produced as follows! the top f the reaction vessel was Sealed 1O Into a quartz glass tube, 5.47 grams of nickel fluoride Then the reaction vessel was tumbled in a large thermo- Powder w lnrredueed- The glass tube Was Plfleed in stat at :0 C. for hohm At the end of this time, an electric furnace and then oxygen gas sufficiently dried methanol containing phenyhhhaphthyl amine Was poured 'by passage through calcium chloride and molecular sieves into the reaction vessel to precipitate the Polymer. The was streamed into the tube. The tube was gradually heated precipitate was redissolved in toluene and then precipiandowas mamtamed e a temperature between and tated again with methanol containing a small amount 560 for 130 mmutese theflrbe was gradeally of dilute hydrochloric acid. The precipitate was separated cooled grams P the QXlde of mekel were Obtalnedand dried at C. for 48 hOurs in vacuo The color of the oxide of nlckel was greenish black. The Rubbery polybutadiene which was completely soluble oxlde of n'lckel had the molecular formula ms and in toluene and gel free was obtained. The yield was 3.18 has actfve oxygen' grams. The microstructure of the polymer was 92.2% W1t h thls catoalystt grams r butadlene were P of cis-1,4, 4.0% of trans-1,4 and 3.8% of vinyl. The in- IYmeHZBdJar 5 f houfs toluene P trinsic viscosity of thfi polymer was drene having an intrinsic viscosity of 2.15 was obtained with a yield of 65.0%. The microstructure was 82.4% of Examples 2 t0 5 c1s-1,4, 13.2% of trans-l,4 and 4.4% of vinyl. Butadiene was polymerized by the same method as in Exam 1e 15 Example 1 except that the ratio of the two catalyst comp ponents was changed. An oxide of nickel having the molecular formula The results are shown In Table 1. NiO was produced 'by oxidizing nickel sulfate by the TABLE 1 N10 AlCl Al/Nl P 1 I2 ti o 1 Example (111111 0?) (mmo l) (mol/mol) tiifih lh on (11 533113 [1,] Mlcrostructme (percent) Cis1,4 Trans-1,4 Vinyl 0 552 0. 553 1.0 20 1 55.0 2.1 o 349 0. 523 1.5 20 1 51.6 2. 02 0 287 0.542 1.89 19 3 11.2 1.92 82 3 12.7 5 0 Examples 6 to '8 same procedure as in Example 14. This oxide of nickel did -In these examples 6.65 grams of butadiene were 40 not e any actlve Oxygeno polymerized by the same procedure as in Example 1, but Butadlerle (665 s) was Polymerlzed at 40 for using an oxide of nickel of the molecular formula NiO hours 111 e f wlth a e y P p y Corl- Which was produced by heating nickel nitrate at 3 50 C tacting 0.254 mrlhmole of the oxide of nickel and 0.512 f 4 hours millimole of aluminum chloride at 60 C. for 2 hours in The polymerization conditions and the results are shown toluene. in Table 2. Polybutadiene was obtained with a yield of 80.1%. The

TABLE 2 Nl01 5 A1013 Al/Ni Polymerization Polymerization Conversion Microstructuue (percent) Example (mmol) (mmol) (mol/mol) time (hr.) temp. 0.) (percent) (Dis-1,4 Trans-1,4 Vinyl 0. 922 0. 461 0. 5 2. 0 40 9. 91. 4 4. 4 4. 2 0.436 0. 436 1. 0 2. 0 40 11.82 88.8 6. 5 4.7 0. 315 0.472 1. 5 2. 0 40 44.12 87.0 7. 7 5. 3

Examples 9 to 13 intrinsic viscosity was 1.96. The microstructure was In these examples, 665 grams of butadiene was 89.1% of cis-1,4, 6.6% of trans-1,4 and 4.3% of vinyl. lymerized with the same procedure as in Example 1, "but using commercially available nickel black.

The polymerization conditions and the results are An oxide of nickel having the molecular formula Example 16 shown in Table 3, NiO was produced by oxidizing nickel chloride by the TABLE 3 Nickel black A1013 Al/Ni Polymer- Polymer- Conversion Microstructure (percent) Ex. (mmol) (mmol) (mol/mol) lzation ization (percent) [a] temp. C.) time (hr.) C1s-1,4 Trans-1,4 Vmyl o. 376 0. 752 2. 0 0 a. 69. 6 2. 2s 87. 6 7. 0 5. 4 0.260 0. 520 2.0 o 4.0 66.6 2. 36 91.6 4.1 4.3 0.405 0 809 2.0 30 3.5 88.9 1.76 88.5 6.9 4.6 0.246 0 429 2.0 30 3.5 82.6 1.98 91.2 4.2 46 13..... 0.123 0 245 2.0 30 5.0 51.2 2. 24 89.2 6.3 4.5

When nickel oxide (NiO) was used instead of nickel same procedure as in Example 14. This oxide of nickel black in Examples 9 and 10, oily products were obtained did not contain any active oxygen. in both runs with a conversion of less than 5%, even Butadiene (6.65 grams) was polymerized at 40 C. for though the polymerizations were carried out for 16 hours 3.5 hours in toluene w1th a catalyst prepared by contactat 0 C. The microstructure of the oily polymers was ing 0.251 millimole of the oxide of nickel and 0.493 milli- '7 8 mole of aluminum chloride at 60 C. for 2 hours in Example 21 toluene Butadiene (6.65 grams) was polymerized at 40 C. for

Polybutadiene having an intrinsic viscosity of 2.12 was 17 hours in 266 grams of n hexane with a catalyst PW,

obtained i a yield of 401% The mlcrostructhre was pared by contacting 0.512 millimole of the oxide of nickel OfC1S-1,4, Of trans-1,4 and Of VlIlyl. 5 olvm) as p p in Example 1 and millinlole E n 17 of aluminum chloride at 60 C. for 1 hour in n-hexane. Polybutadiene was obtained with a yield of 38.1%. The intrinsic viscosity was 2.11. The microstructure was 86.1% of cis-1,4, 9.1% of trans-1,4 and 4.8% of vinyl.

5.2% of the polymer was insoluble in toluene.

In this example, an oxide of nickel was produced by the procedure set forth hereinbelow.

Crystalline nickel sulfate (6.5 grams) and sodium hydroxide (3.0 grams) were dissolved in 100 grams of distilled water. milliliters of 6% by weight aqueous solu- Example 22 tion of S i hyp Was PP the solu' The catalyst was prepared by contacting 0.500'millimole tion- A precipitate fofmed- Th6 preclplfate was W of commercially available nickel black and 0.500 mila fi Washfid and drledgrams of a nlckal P 15 limole of aluminum chloride at 60 C. for 1 hour in 10.1 having the molecular formula )s and Contalnlng grams of toluene. 6.65 grams of butadiene were polymilligram eqiliwlllents of active 3 2 p gram of merized at 40 C. for 4 hours in 26.6 grams of cyclothe peroxide were obtained. Then the nickel peroxide was hexane with the catalyst heated at 700 C. f r 2 hours i the Pfi of Pxygen Polybutadiene having an intrinsic viscosity of 1.41 was In a quartz glass b An OXlde mckel havmg the obtained with a yield of 16.1%. The microstructure of molecular formula N10 Was obtained. 1 g am of t the polymer was 81.9% of cis-1,4, 13.2% of trans-1,4 oxide of nickel contained only 0.004 milligram equivalent d 49% f i 1, of active oxygen.

Butadiene was polymerized by the same method as in Examples 23 to 28 Example 1 except that the catalyst was prepared by IniX- In these examples, the catalysts were prepared by coni g 1.343 millimoles of the oxide of nickel and 0.507 miltacting 0.521 millimole of commercially available nickel limole of aluminum chloride and that the polymerization black and 0.278 millimole of aluminum chloride in 26.6 was carried out at C. for 2 hours. grams of toluene under the conditions shown in Table 5. Polybutadiene having an intrinsic viscosity of 1.51 was 6.65 grams of butadiene were polymerized at 40 C. for obtained with a yield of 74.3%. The microstructure Was 2 hours with these catalysts. Results are shown in Table 5.

TABLE 5 Catalyst preparation condition Conversion Mierostructure (percent) (percent) [1] Temp. C.) Time (min) (Dis-1,4 Trans-1,4 Vinyl 30 300 55. 2 1. 31 88. 2 s. 3. 2 51g 1% 353% 5:12 "hf i f 8. 12.1 it? an a ii 110 120 90.0 2. 92.3 5.8 1 9 82.2% of cis-1,4, 12.4% of trans-1,4 and 5.4% of vinyl. What is claimed is:

On the other hand, when polymerization of butadiene 1. A method for producing a butadiene polyme h was carried out by the same method except that nickel ing a high percentage of cis-1,4 configuration, said method oxide (NiO) produced by heating the nickel peroxide omprising contacting butadiene in the presence of a (Ni(OH) at 1 0 C- r 2 1101118 was p y 45 hydrocarbon solvent at a temperature between C. stead o t e oXlde 0f nlckfil 1.09), I10 Polymer of and 150 C. under an inert gas atmosphere with acatalyst, butadiene could be obtained even after 24 hours. Said catalyst being prepared by mixing, in a hydrocarbon Examples 18 and 19 Solvent under an inert gas atmosphere, 3. halide of alu- Butadiene (6.65 grams) was polymerized in toluene by 50 mmun} an .oxlde of nickel of i hormula Nixoy the same procedure as in Example 1 except that aluminum Wherelh x 15 ah mfeger from 1 to 1s m the range of bromide and iodide were used instead of aluminum chlor- 1 to 3 and the who of to x is in the range 0f 145:1 ide. The conditions for the catalyst preparation were the but excluding a ratio of 1:1; and wherein said Oxide of same as in Example 1. nickel contains no active oxygen capable of oxidizing The polymerization conditions and the results are Potassium iodide at room temperatureshown in Table 4. 2. A method according to claim 1, wherein the con- TABLE 4 NO. Example Aluminum halide (m rniaii i a iih r i i i tih r i ig iigiig [1 (percent) (mmol) temp. 0.) time (hn) (Eds-1,4 Trans-1, 4 Vinyl 18 AlBr 0.553 0. 552 40 3.5 61.2 19 111130.474 0. 473 40 3.5 36.6 81g Example 20 tacting is eflected at a temperature between 0 C. and

Butadiene (6.65 grams) was polymerized at 5 C. for 100 20 hours in 26.6 grams of benzene with a catalyst pre- A .method to h wherein the halide pared by contacting 0.512 millimole of the oxide of nickel of alumlhum and the oxide of hlckel are mixed at a having the molecular formula Niolm as prepared in perature between 20 C. and 150 C. for a period of from ample 1 and 0.512 millimole of aluminum chloride at 1 to 500 minutes- 60 C for 1 h i b 4. A method according to claim 1, wherein the catalyst Polybutadiene was obtained With a yield of 52.3%. The has a mole ratio of aluminum atom to nickel atom within intrinsic viscosity was 2.30. The microstructure was the range of 0.1 to 10.0 to 1.

82.6% of cis-l,4, 12.2% of trans-l,4 and 5.2% of vinyl. 5. A method according to claim 1, wherein the catalyst is present in an amount corresponding to 0.1 to 200 millimoles based on the oxide of nickel per 10 moles of butadiene.

6. A method according to claim 1, wherein the contacting is carried out in the presence of from 0.5 to 50 parts by volume of a hydrocarbon solvent per 1 part by volume of butadiene 7. A method according to claim 1, wherein the halide of aluminum is anhydrous aluminum chloride, bromide or iodide.

8. A butadiene polymerization catalyst consisting of a mixture of a halide of aluminum and an oxide of nickel of the formula Ni O wherein at is an integer from 1 to 2, y is in the range of 1 to 3 and the ratio of y to x is in the range of 1-1.5 :1, but excluding a ratio of 1:1; and wherein said oxide of nickel contains no active oxygen capable of oxidizing potassium iodide at room temperature.

9. A butadiene polymerization catalyst according to claim 8, wherein the halide of aluminum is anhydrous aluminum chloride, bromide or iodide.

References Cited Sidgwick, N. V. Chemical Elements and their Compounds Oxford University Press, pp. 1449-1451 (19 50).

JOSEPH L. SCHOFER, Primary Examiner. R. A. GAITHER, Assistant Examiner.

U.S. Cl. X.R. 

